1) Field of the Invention
The present invention relates to a technology to reduce operation noise of an image forming apparatus.
2) Description of the Related Art
Various kinds of apparatuses that are equipped with an image forming apparatus such as a copying machine, a printer, and a facsimile are installed in a place like an office. The image forming apparatus has a considerable amount of parts mechanically connected to each other. The image forming apparatus also has motors that drive motorized mechanisms. When operated, each part of the image forming apparatus generates operation noise that gives a discomfort to users.
A method of using a sound power level or a sound pressure level as a standard is currently used as a method of evaluating noise generated from the office machines, such as the International Organization for Standard (ISO) 7779. However, according to the method of evaluating noise based on the sound power level or the sound pressure level, a correlation between the evaluation and a subjective discomfort of a human may be low. Therefore, even if the evaluation based on the standard is satisfactory, a person may feel discomfort in many cases.
For example, even when two sounds have the same sound pressure, if a person hears the two sounds having different frequency distributions or different percussive noises may have different discomfort levels from each of the two sounds. In other words, even if the sound pressure level is low, sounds that include a high-frequency component or a pure tone component are apt to be felt unpleasant.
Therefore, it is considered to be necessary to take a measure against the noise of the office machines by evaluating the sound quality and taking the evaluation into account, instead of simply using the sound power level or the sound pressure level as a standard.
Japanese Patent Application Laid-open No. H9-193506 discloses a technique of providing an image forming apparatus with a masking sound generation function to mask the operation noise that is generated during the formation of an image, and decreasing the noise by generating a masking sound during the image forming process.
Japanese Patent Application Laid-open No. H10-232163 discloses a technique of evaluating only rasping as low-frequency random noise that is generated in the airflow such as exhaust sound from among various kinds of sound generated from the image forming apparatus.
Japanese Patent Application Laid-open No. H10-253440 discloses a technique of evaluating only a sound that is generated from a scanner motor or a charger.
Japanese Patent Application Laid-open No. H10-253442 discloses a technique of evaluating only a sound that is generated when a sheet of paper is rubbed as high-frequency random noise.
Japanese Patent Application Laid-open No. H10-267742 discloses a technique of evaluating only a beating sound of a pure tone having a peak in a plurality of close frequencies attributable to the beating of a driving mechanism.
Japanese Patent Application Laid-open No. H10-267743 discloses a technique of evaluating smoothness of sound that includes a pure tone, beating, a low-frequency component, and a high-frequency component that the human feels.
Japanese Patent Application Laid-open No. 2001-336975 discloses a technique of evaluating the sound quality that takes an influence of noise generated from the office machines to a subjective feeling of the human into consideration.
Japanese Patent Application Laid-open No. 2002-128316 discloses an image forming apparatus that has a paper feeding mechanism which obtains a discomfort index based on a loudness and a sharpness obtained from the sound generated from the image forming apparatus, and which makes the obtained discomfort index satisfy a predetermined condition.
However, the image forming apparatus mounted with the masking sound generation function generates the masking sound in addition to sound that the apparatus generates during the operation. Therefore, this has a risk of further increasing the noise level. It is also necessary to install a masking generation unit (such as a speaker, a controller, and a sound source) that has nothing to do with the image forming operation. Accordingly, an installation room is necessary, which prevents implementing a small apparatus, and increases cost. Consequently, this method cannot be an effective countermeasure against the noise.
The above sound quality evaluation techniques enable an evaluation of specific sound quality of the operation noise from the image forming apparatus, by taking into a human's subjective feeling into consideration. However, these techniques do not make clear a detailed method of countermeasures against noise by utilizing a result of the evaluation.
In order to evaluate sound quality and take a countermeasure against the noise based on the result of the evaluation, it is necessary to quantitatively measure the sound quality and measure the improvement in the sound quality after taking the countermeasure in comparison with the sound quality before taking the countermeasure.
However, because the sound quality is not a physical quantity, it is not possible to carry out a quantitative measurement. Therefore, it is difficult to set target variables of improvement. A person evaluates the sound quality as “improved” or “slightly improved”. Since the evaluation levels are different between persons, it is also difficult to determine whether an obtained result is a general evaluation.
Psycho-acoustic parameters are known as physical quantities to evaluate sound quality. The following representative psycho-acoustic parameters are known.
(For example, “targeting for an innovative step of design and system toward the twenty-first century”, The Japan Society of Mechanical Engineers, The seventh design engineering system lecture, “sound, vibration and design, and color and design (1)”, 089B, Nov. 10–11, 1997.)    (1) Loudness (sone): a volume of a hearing    (2) Sharpness (acum): a relative distribution of a high-frequency component    (3) Tonality (tu): a relative distribution of pure tone component    (4) Roughness (asper): a feeling of roughness of sound    (5) Fluctuation strings (vacil): variation strength, a feeling of beating    (6) Impulsiveness (iu): impactness    (7) Relative approach: a feeling of variation
When the values of these parameters increase, the discomfort levels tend to increase.
Since the apparatuses like the copying machine and the printer have a complex structure, these apparatuses generate a sound that includes various kinds of tones. In other words, a plurality of sound sources including a motor, a solenoid, and paper generate time varying low-frequency sound, high frequency sound, and impulsive sound. A human judges whether the sound generated from the image forming apparatus is unpleasant from the total sound. It is considered that a human makes the judgment by placing a weight of discomfort in some portion of the sound. In other words, it is considered that the above kinds of psycho-acoustic parameters do not give discomfort to every person at the same rate, but the parameters have different weights of discomfort.
One of the above conventional techniques provides a paper feeding mechanism that obtains a discomfort index based on a loudness and a sharpness, and makes the obtained discomfort index satisfy a predetermined condition (as disclosed in Japanese Patent Application Laid-open No. 2002-128316). This technique takes the above points into consideration.
Some image forming apparatuses that are available in recent years can select resolution of an image, or can handle both a color image and a monochrome image. Also, some image forming apparatuses can operate differently depending on quality of a paper onto which an image is printed, or can set a printing speed. As explained above, most image forming apparatuses in recent years have a plurality of operation modes. An apparatus that has a plurality of operation modes makes different movements in the parts of the apparatus depending on the operation mode, and the apparatus generates different noises accordingly. Particularly, when the printing speed changes, the frequency component of the sound generated is different according to a change of a motor speed. The sounds generated from each mechanism also changes, and based on the change, a sound source from which a human feels discomfort also changes.
Therefore, for the image forming apparatus that has a plurality of operation modes, it is necessary to take a countermeasure against unpleasant noises in each operation mode by carrying out a complex work to evaluate sound qualities in each operation mode that has a different printing speed. However, the above problems have not yet been solved by the conventional technologies.